Skip to main content

Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

See other formats


ALLOYS  OF LEAD AND TIN

259

paper is treated in a small beaker with 2-3 c.c. of 10% sodium hydroxide
solution and 10-15 c.c. of sodium sulphide (D 1-225), the remaining pro-
cedure being that given for the electrolytic determination of tin in ordinary
bronze (see p. 232).

2. Grammetrically. The filtered and washed metastannic acid precipi-
tate is dried at 100 and removed as far as possible from the filter to a tared
porcelain crucible. The filter-paper is incinerated in a dish, the ash added
to the precipitate, the whole moistened with a few drops of nitric acid, the
excess of acid evaporated and the residue ignited at first with an ordinary
flame and afterwards by means of the blowpipe, and weighed l: Sn02 X
07881 = Sn.

2. Determination of the Lead alone or of the Tin alone.

1.  LEAD ALONE.    This is of interest in some tin-lead alloys composed
mainly of tin, such as solder for culinary utensils and the like.

In a covered electrolytic beaker of 350 c.c. capacity, 1-3 grams of the
alloy as filings are treated, according to the amount of alloy taken, with
6-20 c.c. of fuming nitric acid (D 1-5), 3-9 c.c. of water being then allowed
to flow slowly down the wall of the beaker. When the attack of the metal
is complete, the liquid is boiled for a short time, diluted to about 250 c.c.
and thoroughly mixed with 2-3 grams of copper nitrate or with 1-1-5 gram
of pure copper dissolved in a little nitric acid, the metastannic acid being
allowed to settle and the liquid, without filtering, electrolysed to determine
the lead : Winkler cathode ; matte gauze cylinder anode ; ND100, 0-3 amp.
and voltage, 2-2-2. The cathode should touch the bottom of the beaker,
whilst the anode should not reach to within about I cm. from the layer of
precipitate (for the factor, Pb : Pb02, see p. 258). In this way, even the
small quantities of lead held by the metastannic acid may be liberated by
the current,

2.  TIN ALONE.    In other types of alloy, consisting essentially of lead
(sometimes hard lead)  with small quantities of tin   (0-5-15%), such as
are used for tubes for perfumery, colours, etc., wires for electric valves,
etc., it is of interest to determine the tin alone.

From 2 to 3 grams of the sample in filings or clippings are treated with
20-25 c.c. of boiling cone, sulphuric acid and, when the action is at an end,
the liquid diluted somewhat. When the liquid is cold, 5-6 grams of tartaric
acid are dissolved in it and the whole transferred to a 100 c.c. measuring
flask, made up to volume, and filtered through a dry filter. The tin is
determined in 50 c.c. of the filtrate in the way given for the determination
of tin in hard lead (see p. 248).

*
* *

The composition of solder varies widely with, the metals to be soldered and
with the resistance to be offered to mechanical action, heat, etc. Solders for
coarse work contain about 30% of tin and 70% of lead, whilst those for soft
soldering of small articles contain about 70 % of tin and 30 % of lead ; in some
cases as much as 90% or more of tin are present. The most readily fusible
alloy (183) contains 37% of lead and 63% of tin.

1 In this way any antimony present is calculated as tin,
tin from antimony, see White Metals.

For the separation ofer to which are added 150 c.c. of saturated ammonium bioxalate